The long-term objective of this research is development, optimization and commercial sale of an innovative, rapid and cost-effective screening method for NEOPTERIN and its hydrogenated congeners in body fluids. Ultimately, in Phase II this will take the form of a visible cut-off EIA screen performed directly on a blood spot obtained by finger or ear-stick. Neopterin levels are a sensitive indicator of T-lymphocyte activity and have significance as a screening test of blood donors for infectious diseases and as an early sign of transplant rejection. Immediate objectives of the Phase I feasibility study are: development of polyclonal antibodies of the Phase I feasibility study are: development of polyclonal antibodies to neopterin and its hydrogenated forms (dihydro- and tetrahydroneopterin); development and optimization of an I-125 RIA for total neopterin determination in serum, assessing feasibility for its conversion to neopterin determination in a 1/8" filter paper blood-spot and to neopterin EIA (Phase II development); and preliminary conversion to a prototype RIA for total neopterin in capillary blood on filter paper. This highly innovative new screening test has tremendous potential for commercial and clinical applications which include: AIDS screening--to complement and pre-date HIV positivity, blood donor screening--to exclude acute infectious disease or catastrophic chronic illness when to symptoms are apparent; and transplant rejection--to detect rejection episodes prior to clinical symptoms.